Integrated circuits are formed on a semiconductor substrate by a variety of semiconductor processing methods which provide for a sequence of steps including patterning, additive steps and subtractive steps, in which the integrated circuit structures are formed in a layered manner.
Chemical-mechanical polishing (CMP), sometimes also referred to as chemical-mechanical planarization, is a subtractive method used in semiconductor processing to remove undesired material and provide planar, smooth surfaces on which additional layers may be formed. In general CMP processing involves holding a thin, generally planar, semiconductor substrate (e.g. a wafer) against a rotating polishing surface (e.g. a polishing pad) under controlled pressure. A polishing slurry is supplied to the polishing surface, as a source of abrasive particles and chemical agents for enhancing the polishing process.
Removal of a given material, for instance, a dielectric used to isolate conductors, may be performed in more than one step. For instance, a first polishing step may involve the use of a relatively hard and low compressibility pad to remove the bulk of the undesired dielectric material, followed by a second step which employs a relatively soft pad of high compressibility intended to remove surface defects, such as microscratches, caused by the first polishing step. It is undesirable to have microscratches in the dielectric, because they can be inadvertently filled with conductive materials in subsequent processing steps, which may produce unintended shorts between conductors in the completed circuit.
CMP techniques often form a part of an overall process, sometimes referred to in the art as "damascene", for forming conductors which connect semiconductor devices. The plurality of such conductors along with insulating dielectric, may be referred to as an interconnect structure. Damascene processing involves formation of a dielectric (eg. by deposition) on the substrate, followed by formation of openings in the dielectric and filling of the openings with a conductive material. After each step, CMP is normally used to remove excess material and to planarize the previously filled material.